This invention relates to an electrophotographic photoreceptor which is used in electrophotographic equipment such as a copying machine, a laser beam printer or the like, particularly to an electrophotographic photoreceptor in which an organic photoconductive material is used.
As a photoconductive material for an electrophotographic photoreceptor, there have been used inorganic materials such as selenium (Se), cadmium sulfide (CdS), zinc oxide (ZnO), amorphous silicon (a-Si) and the like. However, a photoreceptor in which such an inorganic material is used is utilized in such a manner that the photoreceptor is charged in a dark place by, for example, a charged roller and then subjected to image exposure to selectively allow only the charge in the exposed portion to disappear, thereby forming an electrostatic latent image, and the latent image is further visualized with a developer to form an image. The basic characteristics required for such an electrophotographic photoreceptor are (1) it can be charged to a suitable potential in a dark place, (2) it has such a function that surface charges can disappear upon light irradiation, and the like. However, the above-mentioned inorganic materials have various advantages and disadvantages. For example, selenium (Se) satisfies sufficiently the above characteristics (1) and (2) but has disadvantages such as inflexibility and difficulty of processing into a film and attention must be paid to its handling because it is sensitive to heat and mechanical shock. Moreover, amorphous silicon (a-Si) has disadvantages such as severe production conditions and, the production cost thereof becomes high.
Therefore, as the electrophotographic photoreceptor, there has recently been mainly used a function-separated type organic photoreceptor which is formed by laminating a charge-transfer layer comprising a hydrazone compound as a charge-transfer agent or the like to a charge-generating layer in which a phthalocyanine or azo compound known as an organic photoconductive material is used as a charge-generating agent.
As a binder resin for such an organic photoreceptor, there has heretofore been most generally used a bisphenol A type polycarbonate resin.
However, when a photosensitive layer is formed by use of a bisphenol A type polycarbonate resin as the binder resin, there is such a disadvantage that the coating solution for the photosensitive layer is gelling or the like. Therefore, a material for the charge-transfer layer freed of such a disadvantage has been desired.
Moreover, the surface of a photosensitive layer in which the above resin is used has a large friction coefficient, so that when an electrophotographic apparatus is fitted with this electrophotographic photoreceptor and an electrophotographic process is repeated in the equipment, there have been caused such inconveniences that the cleaning blade which is generally used in the cleaning of the toner remaining on the photosensitive layer gets recurved, a noise is generated, and the like.
In addition, this polycarbonate resin is inferior in oil resistance, so that during the maintenance of an electrophotographic apparatus or other workings, fingerprints are left on the surface of the photosensitive layer by erroneously touching the surface in some cases, and in such a case, a crack has often been caused in the portion in which the fingerprint is left to make the electrophotographic photoreceptor unusable.
On the other hand, it has been proposed to use a bisphenol Z type polycarbonate resin as a material for the photosensitive layer of an electrophotographic photoreceptor taking the stability of the coating solution into consideration. However, even when this bisphenol Z type polycarbonate resin is used, there have not been solved such problems as the recurving of a blade that results from a large friction coefficient, noise generation, crack formation, and the like.
No material which can solve all the above problems has been found though polycarbonate resins and polycarbonate copolymers having various structures other than the above-mentioned bisphenol A and Z types have been developed as described in, for example, JP-A-4-179,961.
Another problem is that during the maintenance and exchange of an electrophotographic photoreceptor, the electrophotographic photoreceptor is exposed to room light or the like in some cases, and when the electrophotographic photoreceptor is exposed to light for a long period of time, the charge-transfer agent is deteriorated to result in an elevation of the residual potential of the electrophotographic photoreceptor. Such a circumstance becomes a severe obstacle in the simplification of the maintenance. Therefore, maintenance by a skilled serviceman is required and close attention paid thereto.